1. Field of the Invention
This invention relates to portable electronic devices and power sources for such devices.
2. Description of the Related Art
A very large number of important portable electronic devices are becoming available to people throughout the world. Better integrated circuits have greatly reduced the electric energy required to operate these devices and rechargeable batteries are available to power these devices which may be recharged from utility electric sources; however, sometimes such recharging is inconvenient.
Thermoelectric generators are well known. These devices utilize the physics principal known as the Seebeck effect discovered in 1821. If two wires of different materials such as copper and iron are joined at their ends forming two junctions, and one junction is held at a higher temperature than the other junction, a voltage difference will arise between the two junctions. Most thermoelectric generating devices currently in use today utilize semiconductor materials (such as bismuth telluride) which are good conductors of electricity but poor conductors of heat. These semiconductors are typically heavily doped to create an excess of electrons (n-type) or a deficiency of electrons (p-type). An n-type semiconductor will develop a negative charge on the cold side and a p-type semiconductor will develop a positive charge on the cold side. Since each element of a semiconductor thermoelectric device will produce only a few millivolts it is generally useful to arrange the elements in series so as to produce higher voltages. Several techniques have been developed for arranging the semiconductor elements in series in thermoelectric devices. One such method is to use a so-called eggcrate design where a small eggcrate-shaped structure made of insulating material separates the thermoelectric elements and permits the elements to be connected in series in an automated fabrication process to reduce the cost of fabricating these modules and improve reliability. Modules of this design are described in U.S. Pat. No. 5,892,656 that is incorporated herein by reference. The module's (HZ-2) dimensions are 1.15 inches.times.1.15 inches.times.0.20 inch. It will deliver, with a 360 degree F. temperature difference, an open circuit voltage of 6.5 volts and has a design operating range of 2.5 to 4.5 volts with an efficiency of 41/2%. The HZ-2 module is available from Hi-Z Technology, Inc. in San Diego, Calif.
Small portable combustion sources for heat and light have been available for many years. Examples are butane cigarette lighters and portable backpacking stoves where combustion is in the form of a flame. Small catalytic converters are available which will produce a very high temperature without a flame. One device using this technique is a soldering iron.
For many years thermoelectric devices have been used to provide electric power in space vehicles using as a heat source a very small radioactive source and as a cold heat sink the natural coldness of outer space. Use of radioactive sources in populated environments on earth to provide thermoelectric power for portable electronic devices could create problems.
What is needed are portable electronic devices powered with small combustion heat sources.